Image processing system and method, and image display system

ABSTRACT

There is provided an image processing method capable of improving the picture quality. The image processing method comprises: incorporating input frame pictures to be displayed on a display device, on the basis of an input picture signal and an input synchronizing signal which is synchronized with the input picture signal; recording the incorporated input frame pictures in an input frame memory; and producing output frame pictures from input frame pictures, which have been recorded in the input frame memory, by producing an interpolated picture or inserting a black raster picture or thinning out the frame pictures, between input frame pictures corresponding to a picture information of the input frame picture to be displayed, on the basis of the picture information and the input synchronizing signal and an output synchronizing signal.

CROSS REFERENCE TO RELATED APPLICATION

This is a Divisional Application of application Ser. No. 10/970,413,filed Oct. 22, 2004, which is a Divisional Application of applicationSer. No. 09/885,138, filed Jun. 21, 2001, which are based upon and claimbenefit of priority from the prior Japanese Patent Application No.2000-189479, filed on Jun. 23, 2000; the contents of each of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an image processing systemand method, and an image display system.

2. Description of Related Art

As conventional image display devices, there are two-types of impulsetype display devices (e.g., CRTs, field emission type display devices(which will be hereinafter referred to FEDs)), which continue to emitlight only for the afterglow time of a fluorescent substance afterwriting an image, and hold type display devices (e.g., liquid crystaldisplays (which will be hereinafter referred to as LCDs),electroluminescent displays (which will be hereinafter referred to asELDs)), which continue to hold the display of the last frame until a newimage is written. There are also plasma display panels (which will behereinafter referred to as PDPs) and projectors using a film. The PDP isa system for carrying out a gradation display in time axis directions,which is called a pulse width modulation method, so that the PDP isconsidered as a kind of hold type. The projector using a film isconsidered as a hybrid type for carrying out irradiation andnon-irradiation of an image for a frame period. As other systems of ahybrid type, a system using a LCD and a shutter has been proposed byJapan Association of Broadcasters (see Japanese Patent Laid-OpenPublication No. 1997-325715), and a system using a LCD and a flashingback light has been proposed by International Business MachinesCorporation (see Japanese Patent Laid-Open Publication No. 1999-109921).

The hold type display device has a problem in that the blurredphenomenon and the discontinuous display phenomenon are caused duringthe display of a moving picture. As shown in FIG. 16, the blurredphenomenon is caused by the fact that if observer's eyes track themovement of a moving object, the eyes observe the picture while movingon the last frame picture, although the same picture of the last framecontinues to be displayed in a frame before the picture of the nextframe is displayed. That is, the tracking motion of eyes has continuity,so that fine sampling is carried out. As a result, blurring is observedby carrying out visual recognition so that a picture between the firstframe and the second frame is buried. On the other hand, thediscontinuous display phenomenon is particularly observed in the case ofa fixation viewpoint, and is based on the fact that pictures of severalframes are substantially simultaneously observed as shown in FIG. 17.These phenomena depend on the speed of the moving object. If the speedof the moving object increases, the correlation between the last framepicture and the next frame picture deteriorates, so that the phenomenaare more conspicuously observed.

On the other hand, the impulse type display device has a problem in thatthe picture jumping phenomenon is caused during the display of a movingpicture. Although this picture jumping phenomenon is observed similar tothe above described discontinuous display phenomenon, it is described bya different expression since the cause of occurrence is different fromthat of the discontinuous display phenomenon. The picture jumpingphenomenon is also particularly caused at a fixation viewpoint. In theimpulse type display device, since display disappears between frames, inother words, a picture having no correlation right before a next frameis not displayed, so that blurring decreases. On the contrary, thepicture jumping phenomenon is more conspicuously visually recognizedeven in usual observation circumstances. The picture jumping phenomenondepends on the speed of a moving object and a frame frequency (thereciprocal of a frame period). It is considered that the reason why thepicture jumping phenomenon is caused is as follows. If the speed of themoving object increases with respect to the frame frequency, although acorrect image is projected on retinas in time series, the image betweenthe last frame and the next frame disappears as shown in FIG. 18, sothat the interpolation processing is not sufficiently carried out inbrains.

Thus, in conventional image display devices, there is a problem in thatthe picture quality deteriorates in accordance with the displayedcontents. It seems that the deterioration of the picture quality is moreconspicuous with the increase of images having clear contours, i.e.,images including high spatial frequency spectra, such as images obtainedby computer graphics or the like and images picked up by a high-speedshutter video camera.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an image processingmethod comprises: incorporating input frame pictures to be displayed ona display device, on the basis of an input picture signal and an inputsynchronizing signal which is synchronized with the input picturesignal; recording the incorporated frame pictures in an input framememory; and producing output frame pictures from input frame pictures,which have been recorded in the input frame memory, by producing aninterpolated picture or inserting a black raster picture or thinning outthe input frame pictures, between input frame pictures corresponding toa picture information of the input frame picture to be displayed, on thebasis of the picture information and the input synchronizing signal andan output synchronizing signal.

The production of the output frame pictures may comprise: comparing therefresh rate of the input frame pictures with the refresh rate of theoutput frame pictures; outputting the input frame pictures as the outputframe picture, or outputting the input frame pictures, between which theblack raster picture is inserted, as the output frame pictures, when therefresh rate of the input frame pictures is equal to the refresh rate ofthe output frame pictures; producing an interpolated picture between theinput frame pictures, or outputting the input frame pictures, betweenwhich the black raster picture is inserted, as the output framepictures, when the refresh rate of the output frame pictures is higherthan the refresh rate of the input frame pictures; and thinning out theinput frame pictures, or producing an interpolated picture between theinput frame pictures, or outputting the input frame pictures, betweenwhich the black raster picture is inserted, as the output framepictures, when the refresh rate of the output frame pictures is lowerthan the refresh rate of the input frame pictures.

The picture information may include information which indicates whetherthe picture to be displayed is a moving picture or a still picture, andthe method may further comprise discriminating whether the picture to bedisplayed is a moving picture or a still picture.

The discriminating may comprise: incorporating frame pictures of thepicture to be displayed, at regular intervals on the basis of the inputpicture signal and the input synchronizing signal; and obtaining thecorrelation between two input frame pictures which have beencontinuously incorporated, the method discriminating whether the pictureto be displayed is a moving picture or a still picture on the basis ofthe correlation result.

The discriminating may comprise determining whether the moving pictureis in a first state in which the motion of a moving object in the movingpicture is rapid, or in a second state in which the moving speed of themoving object is slower than that in the first state, on the basis ofthe correlation, when it is determined that the picture to be displayedis a moving picture.

The correlation may be obtained on the basis of the difference betweenpixels corresponding to the continuously incorporated two input framepictures.

The correlation may be obtained on the basis of the scalar quantity of amotion vector.

When it is discriminated that the picture to be displayed is a movingpicture and when it is determined that the moving speed of the movingobject in the moving picture is in the first state, the production ofthe output frame pictures may comprise: comparing the refresh rate ofthe input frame pictures with the refresh rate of the output framepictures; outputting the input frame pictures as the output framepicture, when the refresh rate of the input frame pictures is equal tothe refresh rate of the output frame pictures; producing an interpolatedpicture between the input frame pictures to output the interpolatedpicture, when the refresh rate of the output frame pictures is higherthan the refresh rate of the input frame pictures; and thinning out theinput frame pictures to produce and output the output frame pictures,when the refresh rate of the output frame pictures is lower than therefresh rate of the input frame pictures.

The display device may be an impulse type display device, and when it isdiscriminated that the picture to be displayed is a moving picture andwhen it is determined that the moving speed of the moving object in themoving picture is in the second state, the production of the outputframe pictures may comprise: comparing the refresh rate of the inputframe pictures with the refresh rate of the output frame pictures;outputting the input frame pictures as the output frame picture, whenthe refresh rate of the input frame pictures is equal to the refreshrate of the output frame pictures; stopping the output of signalsbetween the input frame pictures, or inserting and outputting a blackraster picture, when the refresh rate of the output frame pictures ishigher than the refresh rate of the input frame pictures; and thinningout the input frame pictures to produce and output the output framepictures, when the refresh rate of the output frame pictures is lowerthan the refresh rate of the input frame pictures.

The display device may be a hold type display device, and when it isdiscriminated that the picture to be displayed is a moving picture andwhen it is determined that the moving speed of the moving object in themoving picture is in the second state, the production of the outputframe pictures may comprise: comparing the refresh rate of the inputframe pictures with the refresh rate of the output frame pictures;outputting the input frame pictures as the output frame picture, whenthe refresh rate of the input frame pictures is equal to the refreshrate of the output frame pictures; stopping the outputs of the outputpicture signal and the output synchronizing signal between the inputframe pictures, when the refresh rate of the output frame pictures ishigher than the refresh rate of the input frame pictures; and thinningout the input frame pictures to produce and output the output framepictures, when the refresh rate of the output frame pictures is lowerthan the refresh rate of the input frame pictures.

When it is discriminated that the picture to be displayed is a stillpicture, the production of the output frame pictures may comprise:comparing the refresh rate of the input frame pictures with the refreshrate of the output frame pictures; outputting the input frame picturesas the output frame picture, when the refresh rate of the input framepictures is equal to the refresh rate of the output frame pictures;displaying the same picture between the output frame pictures, orstopping the output of signals between the input frame pictures, whenthe refresh rate of the output frame pictures is higher than the refreshrate of the input frame pictures; and thinning out the input framepictures to produce and output the output frame pictures, when therefresh rate of the output frame pictures is lower than the refresh rateof the input frame pictures.

The interpolated picture or the black raster picture may be selected inaccordance with the magnitudes of a spatial frequency and frequencyspectra in one frame picture.

Alternatively, the interpolated picture or the black raster picture maybe selected in accordance with the speed of a moving object in thepicture to be displayed.

According to another aspect of the present invention, an imageprocessing system comprises a picture signal converting part convertingan input picture signal, which is a picture signal for a picture to bedisplayed on a display device for displaying a picture while changingthe picture every frame picture, and an input synchronizing signal,which is synchronized with the input picture signal, into an outputpicture signal, which is a picture signal for a picture suitable for thedisplay device, and an output synchronizing signal which is synchronizedwith the output picture signal, on the basis of picture information ofthe picture to be displayed on the display device, the picture signalconverting part comprising: an input frame memory in which a framepicture is recorded; an input switching part transmitting a input framepicture to be displayed, to the input frame memory on the basis of theinput picture signal and the input synchronizing signal; a black rasterpicture producing part in which a black raster picture has been producedor stored; a picture converting part producing output frame picturesfrom input frame pictures, which have been recorded in the input framememory, by producing an interpolated picture or inserting a black rasterpicture or thinning out the input frame pictures, between input framepictures corresponding to the picture information, on the basis of thepicture information and the input synchronizing signal and the outputsynchronizing signal; an output frame memory recording therein theoutput frame pictures; and an output control switching part taking theoutput picture signal and the output synchronizing signal out of theoutput frame pictures, which have been recorded in the output framememory, to transmit the signals to the display device.

The picture signal converting part may include priority processing meansfor spatial-frequency-dividing one frame picture and using aninterpolated picture, not a black raster picture, as an output framepicture, with respect to a picture containing high frequency spectra.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of theembodiments of the invention. However, the drawings are not intended toimply limitation of the invention to a specific embodiment, but are forexplanation and understanding only.

In the drawings:

FIG. 1 is a block diagram showing the construction of the firstembodiment of an image display system according to the presentinvention;

FIG. 2 is a block diagram showing the construction of an embodiment of amotion discriminating part in an image display system according to thepresent invention;

FIG. 3 is a block diagram showing the construction of an embodiment of apicture signal converting part in an image display system according tothe present invention;

FIG. 4 is an illustration for explaining the production of interpolatedpictures which are produced by a picture signal converting part;

FIG. 5 is an illustration for explaining the production of interpolatedpictures which are produced by a picture signal converting part;

FIG. 6 is an illustration for explaining the production of interpolatedpictures which are produced by a picture signal converting part;

FIG. 7 is an illustration for explaining the production of interpolatedpictures which are produced by a picture signal converting part;

FIG. 8 is an illustration for explaining the production of an outputframe picture according to a display system control signal in the firstembodiment;

FIG. 9 is a block diagram showing the construction of the secondembodiment of an image display system according to the presentinvention;

FIG. 10 is an illustration for explaining the production of an outputframe picture according to a display system control signal and a movingpicture/still picture indicating signal in the second embodiment;

FIG. 11 is an illustration for explaining the characteristics of thethird embodiment of a display device with a high-speed refresh rateaccording to the present invention;

FIG. 12 is a block diagram showing the construction of the fourthembodiment of a display device with a high-speed refresh rate accordingto the present invention;

FIG. 13 is an illustration showing an example where effects areparticularly obtained by the fifth embodiment of the present invention;

FIG. 14 is an illustration for explaining a system for deriving themoving speed of a moving object in the sixth embodiment of the presentinvention;

FIG. 15 is a graph showing the relationship between the speed of amoving object and a frame frequency in a display picture in which thepicture jumping phenomenon does not occur;

FIG. 16 is an illustration for explaining the blurred phenomenon in aconventional hold type display device;

FIG. 17 is an illustration for explaining the display discontinuousphenomenon in a conventional hold type display device;

FIG. 18 is an illustration for explaining the picture jumping phenomenonin a conventional impulse type display device;

FIG. 19 is an illustration for explaining the production of an outputframe picture according to a display system control signal in the firstembodiment;

FIG. 20 is an illustration for explaining the production of an outputframe picture according to a display system control signal in the firstembodiment;

FIG. 21 is an illustration for explaining the production of an outputframe picture according to a display system control signal in the firstembodiment;

FIG. 22 is an illustration for explaining the production of an outputframe picture according to a display system control signal in the firstembodiment; and

FIG. 23 is a block diagram showing the construction of the sixthembodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Referring now to the accompanying drawings, the embodiments of thepresent invention will be described below.

First Embodiment

Referring to FIGS. 1 through 7, the first embodiment of the presentinvention will be described below. FIG. 1 shows the construction of thefirst embodiment of an image display system according to the presentinvention. In this embodiment, the image display system comprises animage processing device 1 and a display device with a high-speed refreshrate 50. The image processing device 1 comprises a picture signalconverting part 10, a motion discriminating part 20 and a clockgenerating circuit 30.

The picture signal converting part 10 is designed to convert an inputpicture signal S_(v1) and an input synchronizing signal S_(S1), whichare fed from the side of an image source (e.g., a personal computer, adigital versatile disk (DVD), an NTSC signal source or an HDTV signalsource) on the basis of a display system control signal from the motiondiscriminating part 20 and a clock signal from the clock generatingcircuit 30, into an output picture signal S_(v2) and an outputsynchronizing signal S_(S2), respectively, to transmit the convertedsignals to the display device 50. Furthermore, the input picture signalS_(v1) and the input synchronizing signal S_(S1), and the output picturesignal S_(v2) and the output synchronizing signal S_(S2) are not alwaysthe same as will be described later. The input picture signal S_(v1) andthe input synchronizing signal S_(S1) have a signal type determined bythe image source side, and the output picture signal S_(v2) and theoutput synchronizing signal S_(S2) have a signal type determined by thedisplay device 50. For the converting processing, these signals arelatched by a clock signal CLK which is outputted from the clockgenerating circuit 30. Furthermore, the clock signal CLK for latchingthe above described picture signal and so forth may be inputted to thepicture signal converting part 10 from the outside. In this case, it isnot required to provide the clock generating circuit 30.

The display device 50 is a display device for changing and displaying apicture every frame. If this display device has a multi-scan converter,the horizontal and vertical frequencies of the output picture signalS_(v2) and the output synchronizing signal S_(S2) outputted from thepicture signal converting part 10 are set so as to be frequencies whichare not higher than the maximum horizontal frequency and maximumvertical frequency, respectively, which can be displayed by the displaydevice 50. Therefore, there is provided a multi-frame converter capableof coping with an optional input frame frequency (the vertical frequencyof the input synchronizing signal S_(S1)) and an optional output framefrequency (the vertical frequency of output picture signal S_(v2)) whichis not higher than the maximum vertical frequency which can bedisplayed.

The motion discriminating part 20 will be described below. The motiondiscriminating part 20 is designed to incorporate frame pictures atregular intervals on the basis of the input picture signal S_(v1) andthe input synchronizing signal S_(S1) which are fed from the imagesource, to examine the correlation between continuously incorporated twoframe pictures to determine whether the two frame pictures are movingpictures or still pictures. The determined results are transmitted tothe picture signal converting part 10 as picture information included inthe display system control signal.

FIG. 2 shows the construction of an embodiment of the motiondiscriminating part 20. In this embodiment, the motion discriminatingpart 20 comprises a switch 21, first through n-th n (n≧2) frame memories22 ₁, . . . , 22 _(n) for storing frame pictures, and a differentialsignal detecting part 23. On the basis of the input picture signalS_(v1) and the input synchronizing signal S_(S1) which are fed from theimage source, frame pictures are incorporated at regular intervals bymeans of the switch 21 to be sequentially written in the frame memories22 ₁, . . . , 22 _(n) in time series. The regular intervals means, e.g.,intervals of 1/60 sec. Therefore, the frame numbers of the framepictures stored in the frame memories 22 ₁, . . . , 22 _(n) aredifferent in accordance with the frame frequency of the input picturewhich is fed from the image source to be inputted to the image signalconverting part 10. For example, when the frame frequency of the inputpicture is 60 Hz, the first frame picture is recorded in the first framememory 22 ₁, the second frame picture is recorded in the second framememory 22 ₂, and the n-th (n≧2) frame picture is recorded in the n-thframe memory 22 _(n). Then, the (n+1)-th frame picture is recorded inthe first frame memory 22 ₁. Therefore, the k-th (k≧1) frame picture isrecorded in the r-th frame memory 22 _(r) if a reminder r is not zeroassuming the reminder is r when k is divided by n. Furthermore, when thereminder r is zero, the k-th frame picture is recorded in the n-th framememory 22 _(n). When the frame frequency of the input picture is 240 Hz,the frame pictures are recorded in the frame memories 22 ₁, . . . , 22_(n) at intervals of four frame pictures (at intervals of 1/60 sec).When the frame frequency of the input image is 480 Hz, the framepictures are recorded in the frame memories 22 ₁, . . . , 22 _(n) atintervals of eight frame pictures (at intervals of 1/60 sec).

The frame pictures are thus incorporated at regular intervals (atintervals of 1/60 sec in the above description). Then, on the basis ofthe correlation between these frame pictures, the differential signaldetecting part 23 determines whether the frame pictures are movingpictures or still pictures.

The differential signal determining part 23 is designed to examine thecorrelation between frame pictures by obtaining the difference betweentwo frame pictures, which have been stored in frame memories of twocontinuous numbers (e.g., i-th (i=1, . . . , n−1) frame memory and the(i+1)-th frame memory, or the n-th frame memory and the first framememory), i.e., the difference between picture signals betweencorresponding pixels. It is not required to obtain the difference on thebasis of all of bits of the picture signals (e.g., 8 bits if the picturesignals have 8 bits), but the difference may be detected on the basis ofthe upper 4 bits. In this case, each of the frame memories 22 ₁, . . . ,22 _(n) may be formed so as to be capable of recording only the upper 4bits of the picture signal of each pixel, so that the capacity can besmaller than that when all of bits are recorded.

A method for determining whether frame pictures are moving pictures orstill pictures on the basis of the results of the above describedoperation of the difference will be described below.

If the difference between picture data between corresponding pixels ofthe above described two frame pictures is zero in all of pixels, it maybe determined that the frame pictures are still pictures, and in othercases, it may be determined that the frame pictures are moving pictures.Alternatively, a threshold may be set, and it may be determined that theframe pictures are moving pictures if there is a pixel wherein theabsolute value of the difference is not lower than the threshold.Alternatively, the absolute values of the differences may be summed withrespect to all of pixels or with respect to pixels sampled at regularintervals (e.g., at intervals of three pixels), and it may be determinedthat the frame pictures are moving pictures when the sum is not lessthan the threshold. Furthermore, the determined results are transmittedto the picture signal converting part 10 as information included in thedisplay system control signal.

Referring to FIG. 3, the construction of an embodiment of the picturesignal converting part 10 will be described below. In this embodiment,the picture signal converting part 10 comprises an input switch 12,first through m-th m input frame memories 13 ₁, . . . , 13 _(m), a blackraster picture producing part 14, a picture converting part 15, firstthrough n-th n output frame memories 17 ₁, . . . , 17 _(n), and anoutput control switch 18.

On the basis of the input picture signal S_(v1) and the inputsynchronizing signal S_(S1) which are fed from the image source, framepictures are incorporated by the input switch 12 to sequentiallyrecorded in the first through m-th m input frame memories 13 ₁, . . . ,13 _(m). Furthermore, an input-time address signal indicative of thefact that which input frame memory has stored therein the input framepicture is fed from the input switch 12 to the picture converting part15. On the basis of the synchronizing signals S₁, S₂, the display systemcontrol signal S_(c) from the motion discriminating part 20, and theinput-time address signal from the input switch 12, the pictureconverting part 15 directly outputs the recorded frame pictures asoutput frame pictures, or produces interpolated pictures between twoframe pictures, which have been recorded in the frame memories of twocontinuous numbers, to output the interpolated pictures as output framepictures, or outputs black raster pictures, which have been produced bythe black raster producing part 14, as output frame pictures. The outputframe pictures are sequentially recorded in the first through n-thoutput frame memories 17 ₁, . . . , 17 _(n). Furthermore, an output-timeaddress signal indicative of the fact that which output frame memory hasstored therein the output frame picture is fed from the image convertingpart 15 to the output control switch 18. Then, the recorded output framepictures are fed to the display device with a high-speed refresh rate 50via the output control switch 18 as the output picture signal S_(v2) andoutput synchronizing signal S_(S2).

If the processing time required to prepare an interpolated picture inthe image converting part 15 is the same as the frame pictureincorporating time interval (e.g., 1/60 sec) in the motiondiscriminating part 20, the number m of the input frame memories of thepicture signal converting part 10 shown in FIG. 3 must be 3 (=60/60+2)when the synchronizing signal S_(S1) has 60 Hz, 6 (=240/60+2) when thesynchronizing signal S_(S1) has 240 Hz, and 10 (=480/60+2) when thesynchronizing signal S_(S1) has 480 Hz. The reason why “+2” is added isthat the total two frame memories including a frame memory for preparingan interpolated picture and a frame memory for inputting a new picturewhile preparing the interpolated pictures are required.

When the processing time required to prepare an interpolated picture ishigher than the frame picture incorporating time in the motiondiscriminating part 20, the number m of the input frame memories 13 ₁, .. . , 13 _(m) must be three of two frame memories for inputting twoframe pictures and a frame memory for preparing an interpolated picture.

The operation of the picture signal converting part 10 will be describedbelow. The conversion of a picture signal is basically determined bycomparing the vertical frequency of an input synchronizing signal S_(S1)(the refresh rate of an input frame picture) and the vertical frequencyof an output synchronizing signal S_(S2) (the refresh rate of an outputframe picture).

When the refresh rate of the input frame picture is equal to the refreshrate of the output frame picture, it is not required to produce aninterpolated picture as the output frame picture, and input framepictures having been sequentially recorded in the first through m-thinput frame memories 13 ₁, . . . , 13 _(m) are sequentially fed directlyto the first through n-th output frame memories 17 ₁, . . . , 17 _(n) asoutput frame pictures to be recorded therein. Alternatively, input framepictures, which have been sequentially recorded in the first throughm-th input frame memories 13 ₁, . . . , 13 _(m) and between which blackraster pictures have been inserted, are sequentially fed to the firstthrough n-th output frame memories 17 ₁, . . . , 17 _(n) as output framepictures to be recorded therein. Then, the output frame pictures, whichhave been recorded in the first through n-th output frame memories 17 ₁,. . . , 17 _(n), are taken out via the output control switch 18 asoutput picture signals S_(v2) and output synchronizing signals S_(s2) tobe transmitted to the display device 50.

On the other hand, when the refresh rate of the output frame picture ishigher than the refresh rate of the input frame picture, it is requiredto increase the number of frames. Therefore, interpolated pictures areproduced, or black raster pictures are inserted. Referring to FIGS. 4through 7, the production of the interpolated pictures will be describedbelow.

FIG. 4 is an illustration for explaining the production of interpolatedpictures when the refresh rate of an input frame picture is 360 Hz andthe refresh rate of an output frame picture is 480 Hz, and FIG. 5 is anillustration for explaining a method for inputting the input framepicture to the input frame memory and a method for inputting the outputframe picture to the output frame memory at this time.

First, as shown in FIG. 5, after input frame pictures A, B and C areinputted to the first, second and third input frame memories 13 ₁, 13 ₂and 13 ₃, respectively, to be recorded therein, input frame pictures D,E and F are repeatedly recorded in the first, second and third inputframe memories 13 ₁, 13 ₂ and 13 ₃, respectively. The input control ofeach of the input frame pictures is carried out by the input switch 12.

An input-time address signal indicative of the relationship between aninput frame picture and an input frame memory is fed from the inputswitch 12 to the picture converting part 15. Then, the pictureconverting part 15 produces an input picture from the input framepicture while adjusting the time axis. For example, the input framepicture A is fed to the first output frame memory 17 ₁ as an outputframe picture a without being picture-converted by the pictureconverting part 15, to be recorded therein (see FIGS. 4 and 5). Theintervals of one frame between the input frame picture and the outputframe picture are different by 1/1440 sec (= 1/360− 1/480). Therefore,the picture converting part 15 produces an interpolated picture, whichis shifted in the direction of the time axis (shifted in advance of theinput frame picture B by 1/1440 sec), from the input frame pictures Aand B on the basis of the input-time address signal, and theinterpolated picture thus produced is outputted as an output framepicture b (see FIG. 4) to be recorded in the second output frame memory17 ₂ (see FIG. 5). Furthermore, while the interpolated picture b isproduced, the input frame picture C is inputted to the third input framememory 13 ₃ to be recorded therein (see FIG. 5). In addition, while theinterpolated picture b is recorded in the second output frame memory 17₂, the output frame picture a is outputted as an output picture signalS_(v2) via the output control switch 18.

After the production of the interpolated picture b is completed and therecording of the input frame picture C in the third frame memory 13 ₃ iscompleted, an interpolated picture c, which is shifted in the directionof the time axis (shifted in advance of the input frame picture C by1/720 sec) from the input frame pictures B and C, is produced, and theinterpolated picture c thus produced is outputted as an output framepicture c to be recorded in the first output frame memory 17 ₁ (see FIG.5).

Furthermore, while the interpolated picture c is produced, the inputframe picture D is inputted to the first input frame memory 13 ₁ to berecorded therein (see FIG. 5). In addition, while the interpolatedpicture c is recorded in the first output frame memory 17 ₁, the outputframe picture b is outputted as an output picture signal S_(v2) via theoutput control switch 18.

After the production of the interpolated picture c is completed and therecording of the input frame picture D is completed, an interpolatedpictured, which is shifted in the direction of the time axis, isproduced from the input frame pictures C and D, and is recorded in thesecond output frame memory 17 ₂ as an output frame picture d (see FIGS.4 and 5). Furthermore, while the interpolated picture d is produced, theinput frame picture E is recorded in the second frame memory 13 ₂ (seeFIG. 5). In addition, while the interpolated picture d is recorded, theoutput frame picture c is outputted as an output picture signal S_(v2)via the output control switch 18.

Subsequently, the input frame picture D is directly outputted as anoutput frame picture e to be recorded in the first output frame memory17 ₁. At this time, an input frame picture F is inputted to the thirdinput frame memory 13 ₃ to be recorded therein, and an output framepicture d is outputted as an output picture signal S_(v2) from thesecond output frame memory 17 ₂ via the output control switch 18. Thus,it is possible to obtain output frame pictures from input framepictures.

Since it is assumed in FIGS. 4 and 5 that the input frame picture A isthe same as the output frame picture a, the number of input framememories and the number of output frame memories can be reduced by 5frames, respectively. As can be seen from FIG. 4, since one output framepicture is prepared from two input frame pictures, it is possible toreduce three frames for input frame pictures (in order to input apicture to another frame memory while two frame pictures are processed),and two frames for output frame pictures (two frames are required whenthe writing and reading of output frame pictures in and out of the sameframe memory can not simultaneously be carried out). Furthermore, inthis case, the producing speed of the interpolated picture must be equalto the frequency of the input picture.

On the other hand, when the refresh rate of the output frame picture ishigher than the refresh rate of the input frame picture, frame picturesare thinned out, or interpolated pictures are produced, or black rasterpictures are inserted. When the refresh rate of the input frame pictureis an integer times as large as the refresh rate of the output framepicture (e.g., when the refresh rate of the input frame picture is 480Hz and the refresh rate of the output frame picture is 240 Hz), framepictures can be simply thinned out on alternate frame pictures as shownin FIG. 6. In other cases (e.g., when the refresh rate of the inputframe picture is 480 Hz and the refresh rate of the output frame pictureis 360 Hz), interpolated pictures are produced as shown in FIG. 7. Theproduction of interpolated pictures may be carried out in the samemanner as the above described manner. An interpolated picture b, whichis shifted in the direction of the time axis (shifted behind the framepicture B by 1/1440 sec), is produced from the input frame pictures Band C. This is used as an output frame picture b, and an output framepicture c is sequentially prepared from the input frame pictures C andD. Since it is also assumed in FIG. 7 that the input frame picture A isthe same as the output frame picture a, the number of input framememories and the number of output frame memories can be reduced by sixframes. In addition, as can be seen from FIG. 7, since one output framepicture is prepared from two input frame pictures, it is possible toreduce three frames for input frame pictures (in order to input apicture to another frame memory while two frame pictures are processed),and two frames for output frame pictures (two frames are required whenthe writing and reading of output frame pictures in and out of the sameframe memory can not simultaneously be carried out).

As another information required to produce a display system controlsignal, there is a signal indicative of the fact that the display device50 is an impulse type or a hold type. This signal is received from theconnected display device 50. An example of a picture outputted from thisdisplay system will be described later. In the black raster pictureproducing part 14, this signal is used for producing a picture which isdisplayed during a reset period when the hold type display device istechnically used as an impulse type display device. Furthermore,according to the present invention, the black raster picture must notalways be black, but it may be blue or magenta which has a lowluminosity factor. In order to maintain contrast, the black rasterpicture is preferably in a display state in which the emission luminanceor reflection luminance is low. According to the present invention, thedisplay device with a high-speed refresh rate 50 may be effectively atransmission type display device or a reflection type display device.

On the basis of the display system control signal, the picture signalconverting part 10 controls the output picture signal and outputsynchronizing signal as follows. For example, when it is determined thatthe display pictures are still pictures, it is assumed that the signalis a signal for indicating the output of an output picture signal and anoutput synchronizing signal, and when it is determined that the displaypictures are moving pictures, it is assumed that the signal is a signalfor indicating the output of an interpolated picture and an outputsynchronizing signal or a signal for indicating the output of a blackraster picture or an output synchronizing signal with respect to a holdtype display device, and a signal for indicating the stopping of theoutput of an output picture signal and an output synchronizing signal orthe output of an interpolated picture and an output synchronizing signalwith respect to an impulse type display device. The display systemcontrol signal basically indicates the discriminated results of a movingpicture or a still picture. However, as described above, since theindicating method is different in accordance with the kind of thedisplay device (hold type or impulse type), a signal indicative of ahold type or an impulse type can be previously inputted from the displaydevice to the motion discriminating part to set it by a combination ofthe discriminated result of moving/still picture and the kind of thedisplay device.

Furthermore, in the motion discriminating part 20 in this embodiment, adifferential signal of each of frames is taken. When the variation islarge, it is determined that the display pictures are rapid movingpictures. When the variation is small, it is determined that the displaypictures are slow moving pictures. When there is no variation, it isdetermined that the display pictures are still pictures. The system fordetermining the moving speed of the moving picture in the motiondiscriminating part 20 may be the same as a system which will bedescribed later in the second embodiment. The discriminated result isfed to the output control switch 18 as a display system control signal,and an output picture (an output picture signal and an outputsynchronizing signal) to the display device 50 is prepared in accordancewith a signal indicative of a display system and a moving/still pictureindicating signal.

Referring to FIG. 8, the production of an output frame picture accordingto a display system control signal Sc in the picture signal convertingpart 10 in the first embodiment will be described below. In thedescription herein, it is assumed that the refresh rate of an inputframe picture is 60 Hz and the refresh rate of an output frame pictureis 480 Hz (see FIG. 8).

It is also assumed that the display device is an impulse type displaydevice. In this case, when the motion discriminating part 20 determinesthat the display pictures are rapid moving pictures, interpolatedpictures a1, a2, . . . , a7 which are interpolated between the inputframe pictures A and B are produced as shown in FIG. 8( b). That is, theinput frame picture A is directly outputted as an output frame picture,the input frame picture B is directly outputted as an output framepicture b, and seven frame pictures therebetween are outputted as theinterpolated pictures a1, a2, . . . , a7 as described above. When themotion discriminating part 20 determines that the display pictures areslow moving pictures, after the input frame picture A is outputted asthe output frame picture a, until the input frame picture B is outputtedas the output frame picture b, black raster pictures r1, . . . , r7 areoutputted, or the output of the output picture signal S_(v2) and theoutput synchronizing signal S_(s2) is stopped, as shown in FIG. 8( c).When the motion discriminating part 20 determines that the displaypictures are still pictures, after the input frame picture A isoutputted as an output frame picture, black raster pictures r_(s) areoutputted as the second to fourth output frame pictures, and the outputframe picture a is outputted as the fifth output frame picture, or thesame picture a is outputted over eight frames, as shown in FIG. 8( d).

On the other hand, when the display device is a hold type displaydevice, if it is determined that the display pictures are rapid movingpictures, an interpolated picture which is interpolated between theinput frame pictures is outputted as an output frame picture as shown inFIG. 8( b). If it is determined that the display pictures are slowmoving pictures, after the output frame picture a is outputted, blackraster picture signals are outputted in the second to eighth framesuntil the output frame picture b is outputted, as shown in FIG. 8( c).If it is determined that the display pictures are still pictures,although the output frame pictures may be outputted as shown in FIG. 8(c) or FIG. 8( d), the outputs of the output picture signal and theoutput synchronizing signal are stopped instead of the black rasterpicture signal. Therefore, in this case, the output frame picture acontinues to be held.

While the production of output frame pictures according to the displaysystem control signal Sc in the picture signal converting part 10 hasbeen briefly described referring to FIG. 8, this will be described inmore detail referring to FIGS. 19 through 22. In this embodiment, thedisplay method can be changed in accordance with the results ofcomparison of the refresh rate of the input frame picture with therefresh rate of the output frame picture in the picture signalconverting part 10 and the results of discrimination in the motiondiscriminating part 20.

First, a case where the display device with a high-speed refresh rate 50is an impulse type display device will be described below.

i) Referring to FIG. 19, a case where the motion discriminating part 20determines that the display pictures are moving pictures will bedescribed below.

1) When the refresh rate of the input frame picture is equal to therefresh rate of the output frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 240 Hz, input frame pictures A, B, C, D and E shown inFIG. 19( a) are directly outputted as output frame pictures a, b, c, dand e as shown in FIG. 19( b).

2) When the refresh rate of the output frame picture is higher than therefresh rate of the input frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 480 Hz, if the motion discriminating part 20 determinesthat the display pictures are rapid moving pictures, interpolatedpictures are produced and outputted between input frame pictures shownin FIG. 19( a) (see FIG. 19( c)). That is, interpolated pictures a′, . .. are produced and outputted between the output frame pictures, a, b, .. . corresponding to the input frame pictures A, B, . . . . In FIG. 19(c), the frame picture a′ is an interpolated picture between the outputframe pictures a and b.

3) When the refresh rate of the output frame picture is higher than therefresh rate of the input frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 480 Hz, if the motion discriminating part 20 determinesthat the display pictures are slow moving pictures, the output of thepicture signal between the output frame pictures a, b, c, d and e isstopped, or black raster pictures are inserted between the output framepictures a, b, c, d and e corresponding to the input frame pictures A,B, C, D and E as shown in FIG. 8( c). When the output of the picturesignal between the output frame pictures is stopped, nothing isdisplayed while the picture a′ of FIG. 19( c) is displayed (not shown).In this case, the luminance of the screen varies by changing thepresence of the display during the display of the picture a′. In orderto avoid this, the picture a may be directly displayed during thedisplay of the picture a′ as shown in FIG. 19( d).

4) When the refresh rate of the input frame picture is higher than therefresh rate of the output frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 60 Hz, the output frame pictures b, c and dcorresponding to the input frame pictures B, C and D are thinned out tooutput picture signals as shown in FIG. 19( e).

ii) Referring to FIG. 20, a case where the motion discriminating part 20determines that the display pictures are still pictures will bedescribed below.

1) When the refresh rate of the input frame picture is equal to therefresh rate of the output frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 240 Hz, input frame pictures A, B, C, D and E shown inFIG. 20( a) are directly outputted as output frame pictures a, b, c, dand e as shown in FIG. 20( b).

2) When the refresh rate of the output frame picture is higher than therefresh rate of the input frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 480 Hz, the same picture is displayed between theoutput frame pictures as shown in FIG. 20( c) (e.g., the picture a isdisplayed between the output frame pictures a and b). Alternatively,when the frequency of the display device with a high-speed refresh rateis high as this case (e.g., when it is 240 Hz or higher), the output ofsignals between pictures is stopped, and nothing is displayed while,e.g., the picture a of FIG. 20( c), is displayed. In the latter, thefrequency of flicker is 120 Hz (half of 240 Hz), there is no problem onflicker.

3) When the refresh rate of the input frame picture is higher than therefresh rate of the output frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 60 Hz, the output frame pictures b, c and dcorresponding to the input frame pictures B, C and D are thinned out tooutput picture signals as shown in FIG. 20( d).

Then, a case where the display device with a high-speed refresh rate 50is a hold type display device will be described below.

i) Referring to FIG. 21, a case where the motion discriminating part 20determines that the display pictures are moving pictures will bedescribed below.

1) When the refresh rate of the input frame picture is equal to therefresh rate of the output frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 240 Hz, input frame pictures A, B, C, D and E shown inFIG. 21( a) are directly outputted as output frame pictures a, b, c, dand e as shown in FIG. 21( b).

2) When the refresh rate of the output frame picture is higher than therefresh rate of the input frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 480 Hz, if the motion discriminating part 20 determinesthat the display pictures are rapid moving pictures, interpolatedpictures a′, . . . are produced and outputted between the output framepictures, a, b, c, d and e corresponding to the input frame pictures A,B, C, D and E as shown in FIG. 21( c), or a black raster picture r isinserted as shown in FIG. 21( d).

3) When the refresh rate of the output frame picture is higher than therefresh rate of the input frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 480 Hz, if the motion discriminating part 20 determinesthat the display pictures are slow moving pictures, the output of thepicture signal between pictures is stopped, and an output control signal(not shown) in the hold type display device is deactivated. Thus, forexample, in an LCD, gate lines are not in ON state to prevent writing inpixels. Thus, the picture a continues to be displayed while theinterpolated picture a′ shown in, e.g., FIG. 21( c), is displayed (notshown).

4) When the refresh rate of the input frame picture is higher than therefresh rate of the output frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 60 Hz, the output frame pictures b, c and dcorresponding to the input frame pictures A, B, C, D and E are thinnedout to output picture signals as shown in FIG. 21( e).

ii) Referring to FIG. 22, a case where the motion discriminating part 20determines that the display pictures are still pictures will bedescribed below.

1) When the refresh rate of the input frame picture is equal to therefresh rate of the output frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 240 Hz, input frame pictures A, B, C, D and E shown inFIG. 22( a) are directly outputted as output frame pictures a, b, c, dand e as shown in FIG. 22( b).

2) When the refresh rate of the output frame picture is higher than therefresh rate of the input frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 480 Hz, the same picture is displayed between theoutput frame pictures a, b, c, d and d corresponding to the input framepictures A, B, C, D and E as shown in FIG. 22( c) (e.g., the picture ais displayed between the output frame pictures a and b). Alternatively,the outputs of the output picture signal and the output synchronizingsignal between pictures are stopped, and an output control signal (notshown) in the hold type display device is deactivated. Thus, forexample, in an LCD, gate lines are not in ON state to prevent writing inpixels. At this time, the display state is the same as that shown inFIG. 22( c).

3) When the refresh rate of the input frame picture is higher than therefresh rate of the output frame picture, e.g., when the refresh rate ofthe input frame picture is 240 Hz and the refresh rate of the outputframe picture is 60 Hz, the output frame pictures b, c and dcorresponding to the input frame pictures B, C and D are thinned out tooutput picture signals as shown in FIG. 22( d).

As described above, according to this embodiment, output picture signalscorresponding to the display device 50 can be produced from inputpicture signals, and output frame pictures can be produced in accordancewith the fact that a display picture is a moving picture or a stillpicture, so that it is possible to improve the picture quality.

Second Embodiment

Referring to FIGS. 9 and 10, the second embodiment of the presentinvention will be described below. FIG. 9 shows the construction of thesecond embodiment of an image display system according to the presentinvention. The image display system 1A in the second embodiment is thesame as the image display system 1 in the first embodiment, except thata moving/still picture indicating part 40 is further provided. Themoving/still picture indicating part 40 is designed to transmit amoving/still picture indicating signal, which indicates whether the kindof a display picture displayed on the display device 50 is a movingpicture or a still picture, to the picture signal converting part 10.

The moving/still picture indicating part 40 takes a system fordetermining a picture signal by an input synchronizing signal (e.g.,determination of NTSC (National Television System Committee) system orPAL (Phase Alternation by Line) system, HDTV (High DefinitionTelevision) system), or receiving a signal indicative of an operatingapplication software (e.g., an application software for reproduction ofmoving pictures, an application software for reproduction of stillpictures) or a signal indicative of a reproduced file (e.g., extension)to determine a moving/still picture by a correspondence table which isprovided in the moving/still picture indicating part 40.

The moving/still picture indicating part 40 may basically serve todetermine motion during a predetermined period of time similar to themotion discriminating part 20. However, there are some cases where amoving picture may be displayed during a longer period of time than apredetermined period of time for a processing carried out by the motiondiscriminating part 20, in some image sources. In such cases, it isdetermined that the display picture is a still picture in spite of amoving picture since the same picture is recorded in the input framememory in the motion discriminating part 20. Thus, blurring may occurson the moving picture in the hold type display device. Therefore, thepicture signal converting part 10 is designed to receive a moving/stillpicture indicating signal, which indicates whether the display pictureis a moving picture or a still picture, from the moving/still pictureindicating part 40.

Referring to FIG. 8, the production of an output frame picture accordingto a display system control signal and a moving/still picture indicatingsignal in the picture signal converting part 10 in the second embodimentwill be described below. It is herein assumed that the refresh rate ofan input frame picture is 60 Hz and the refresh rate of an output framepicture is 480 Hz.

For example, if the display device 50 is an impulse type display device,when the moving/still picture indicating signal indicates a stillpicture and when the motion discriminating part 20 determines that thedisplay picture is a rapid moving picture (e.g., when the whole screenis switched), an output picture is selected as shown in FIG. 8( d). Whenthe motion discriminating part 20 determines that the display picture isa slow moving picture (e.g., when the screen is scrolled), an outputpicture is selected as shown in FIG. 8( b), and when the motiondiscriminating part 20 determines that the display picture is a stillpicture, an output picture is selected as shown in FIG. 8( d). On theother hand, when the moving/still picture indicating signal indicates amoving picture and when the motion discriminating part 20 determinesthat the display picture is a rapid moving picture (e.g., when a movingobject which moves rapidly exists), an output picture is selected asshown in FIG. 8( b), and when the motion discriminating part 20determines that the display picture is a slow moving picture (e.g., whena moving object which moves slowly exists), an output picture isselected as shown in FIG. 8( c). If the motion discriminating part 20determines that the display picture is a still picture, informationthereon is ignored, and an output picture is selected as shown in FIG.8( c). The reason why the output picture shown in FIG. 8( c) is selectedis that no interpolated picture can be prepared. A system fordetermining the moving speed of the moving picture in the motiondiscriminating part 20 may be the same as that in the first embodiment.Alternatively, when the difference between information in an input framememory, which has been most newly inputted, and those in other inputframe memories is large, it may be determined that motion is rapid, andwhen the difference between information in the input frame memory, whichhas been most newly inputted, and the oldest input frame memory issmall, it may be determined that motion is slow.

If a motion vector such as MPEG4 is used, it is possible to determinewhether the motion of a moving picture is rapid or slow on the basis ofthe magnitude of the vector. Systems for interpolating pictures includea system for extracting a changing region and picture information afterchange from a motion vector in MPEG4 to replace the changing region withpicture information in a frame memory (see Japanese Patent Laid-OpenPublication No. 2000-284755), and an interpolation system (see JapanesePatent Laid-Open Publication No. 1995-107465). The detailed descriptionsthereof are herein omitted. The entire contents of these references areincorporated by references.

Referring to FIG. 19, a case where the display device 50 is a hold typedisplay device will be described below. In this case, it is assumed thatthe refresh rate of an input frame picture is 480 Hz and the refreshrate of an output frame picture is 120 Hz (see FIG. 10).

When the moving/still picture indicating signal indicates a stillpicture, an output picture is selected as shown in FIG. 10( d). When themoving/still picture indicating signal indicates a moving picture andwhen the motion discriminating part 20 determines that the displaypicture is a rapid moving picture (e.g., when a moving object whichmoves rapidly exists), an output picture in which pictures are thinnedout is selected as shown in FIG. 10( b). When the motion discriminatingpart 20 determines that the display picture is a slow moving picture(e.g., when a moving object which moves slowly exists), an outputpicture in which a black raster picture is inserted is selected as shownin FIG. 10( c). when the moving/still picture indicating signalindicates a moving picture and when the motion discriminating part 20determines that the display picture is a still picture, informationthereon is ignored, and the output picture shown in FIG. 10( c) isselected.

When the moving/still picture indicating signal indicates a stillpicture or when the motion discriminating part 20 determines that thedisplay picture is a still picture, the characteristics of the hold typedisplay device may be utilized for outputting the picture of the firstoutput frame memory 181, and then, the output may be stopped. Also bythis method, it is possible to provide a picture having no flicker.

As described above, according to the image display system in the secondembodiment, output frame pictures are outputted in accordance with thefact that a display picture is a rapid moving picture, a slow movingpicture or a still picture, so that it is possible to improve thepicture quality.

In addition, by providing the moving/still picture indicating part 40,the hold type display device can prevent blurring from occurring on amoving picture even if the moving picture is displayed for a longerperiod of time than a predetermined period of time for a processingcarried out in the motion discriminating part 20, so that it is possibleto improve the picture quality.

Third Embodiment

Referring to FIG. 11, the third embodiment of an image display systemaccording to the present invention will be described below. In the thirdembodiment, the image display system is the same as the image displaysystem in the first or second embodiment, except that the display devicewith a high-speed refresh rate 50 comprises a CRT having a fluorescentsubstance or an impulse type display device such as FED.

This embodiment is characterized in that when output pictures shown inFIGS. 8( c), 8(d) and 10(c) are displayed, the output of an outputpicture signal S_(v2) and an output synchronizing signal is stopped toprovide a non-emission period in place of the output of a black rasterpicture. In the display device using a fluorescent substance, therelationship between the afterglow time of the fluorescent substance anda frame period should be noted. As shown in FIG. 11( b), a firstfluorescent substance having a shorter afterglow time than the frameperiod is used. When a second fluorescent substance having a longerafterglow time than the frame period is used, there are some cases wherethe screen is gradually brightening as shown in FIG. 11( c), so that itis required to limit the maximum driving voltage Vdrv of the displaydevice (the maximum variation in cathode voltage and cut-off voltage).

There may also be a problem in that the brightness of the screen isdifferent by changing the display system. For example, in FIG. 8, thebrightness of the output pictures shown in FIG. 8( d) is double as largeas the brightness of the output pictures shown in FIG. 8( c), and thebrightness of the output picture shown in FIG. 8( c) is eight times aslarge as the brightness of the output pictures shown in FIG. 8( c).Therefore, the mean brightness of the screen must be equal to each otherto some extent. This is particularly important when the display systemis frequently changed, and the difference between the luminance valuesof the respective display systems must be about 1%. In the displaydevice with a high-speed refresh rate using CRT, both of contrast andcolor purity can be adjusted by controlling the maximum driving voltageVdrv and the cut-off voltage Ek-co for beams. In the FED, these can beadjusted by the anode voltage. These set values may be previouslyrecorded in the memory of the display device with a high-speed refreshrate, and read in accordance with a display system control signal fromthe motion discriminating part 20. It is also preferred that picturesignals may be changed in accordance with the display system instead ofchanging the set values of the display device. For example, the outputpicture signals shown in FIG. 8( d) may be changed so that its luminancevalue is a half of that of output picture signals shown in FIG. 8( c).

Also in the third embodiment, it is possible to improve the picturequality.

Fourth Embodiment

Referring to FIG. 12, the fourth embodiment of an image display systemaccording to the present invention will be described below. In thefourth embodiment, the image display system is the same as the imagedisplay system in the first or second embodiment, except that thedisplay device with a high-speed refresh rate is a hold type displaydevice, such as an LCD or an ELD with memory elements.

In this embodiment, when output pictures shown in FIGS. 8( c), 8(d) and10(c) are displayed, a black raster picture is outputted in the case ofa frame picture to which the black raster picture is to be outputted.

However, the ELD used herein has memory elements capable of recordingtherein a signal to the respective pixel electrode every pixel, and iscited as an example of a display device wherein display information isnot rewritten until a next signal to the respective pixel electrode iswritten again although this principle is different from that of LCDs.This embodiment will be described using an LCD which is a typicalexample of a hold type. Liquid crystal materials for use in LCDs includetwist nematic liquid crystals, ferroelectric liquid crystals (which willbe hereinafter referred to as FLCS), and optically compensated bendmodes (which will be hereinafter referred to as OCBs) which aim at afast response. In particular, FLCs and OCBs can carry out a high-speedrefresh display due to their fast response. As shown in the figure, theimage display system in this embodiment comprises a signal line drivingcircuit 62 for supplying signals to the respective pixel electrodes ofliquid crystal cells, a reset voltage output part 65 capable ofresetting (making a black display state) all of pixels on the same gateline as a gate line driving circuit 63 for driving gate lines which areconnected to the respective pixel electrodes in row directions viaswitching elements for writing every row, and a liquid crystal displaypanel 61. Since the array construction of the liquid crystal displaypanel 61 is well known, the detailed description thereof is omitted. Anoutput picture signal and an output synchronizing signal are inputted tothe signal line driving circuit 62, and signals are simultaneouslyoutputted to pixels in row directions in synchronism with thesynchronizing signal. The gate driving circuit 63 also receives theoutput synchronizing signal to sequentially scan on gate lines in columndirections. The liquid crystal display device uses a display system forcontinuing to hold the last picture until the next gate line is scanned.For example, when output pictures shown in FIGS. 8( c) and 8(d) aredisplayed, a black raster picture may be inputted as an output picturesignal, or a reset indicating signal may be inputted to the resetvoltage output part 65 from the output control switch 18 in synchronismwith the output synchronizing signal to display black with respect toall of pixels. In this case, there are a method for sequentiallyscanning gate lines to sequentially change the display to a black rasterdisplay every one line, and a method for simultaneously scanning all ofgate lines from the gate line driving circuit 63 to simultaneouslychange the display to a black display with respect to all of pixels.

Although there may also be a problem in that the brightness of thescreen is different by changing the display system, another light valve(which may be a liquid crystal panel) capable of varying the luminanceof a back light in accordance with a frame frequency or of varyingtransmittance can be arranged on the front face of the liquid crystalpanel. Also in this case, similar to the third embodiment, set valuesare previously recorded in the memory of the display device with ahigh-speed refresh rate, and the luminance of the back light or avoltage applied to the other light valve is controlled in accordancewith the display system control signal from the motion discriminatingpart.

It is also preferred that picture signals may be changed in accordancewith the display system instead of changing the set values of thedisplay device. For example, the output picture signals shown in FIG. 8(d) may be changed so that its luminance value is a half of that ofoutput picture signals shown in FIG. 8( c).

Also in the fourth embodiment, it is possible to improve the picturequality.

Fifth Embodiment

Referring to FIG. 13, the fifth embodiment of an image display systemaccording to the present invention will be described below. In the imagedisplay system in the fifth embodiment, the frame frequency of thedisplay device with a high-speed refresh rate is set to be 240 Hz orhigher in the image display system in the first or second embodiment.According to the inventor's experiments, it was confirmed that it waspossible to improve the picture quality in most of moving pictures bysetting the frame frequency of the display device with a high-speedrefresh rate to be 240 Hz or higher.

For example, in the case of a so-called scrolled picture wherein thewhole screen moves as shown in FIG. 13( a), a picture wherein a rapidmoving object (a person in the figure) exists in a stopped background (ahouse in the figure) as shown in FIG. 13( b), and a picture wherein themoving speed of a moving object relatively increases since thebackground and the moving object move in opposite directions as shown inFIG. 13( c), it was confirmed that it was possible to make the picturequality of the moving picture smooth to improve the picture jumpingphenomenon by setting the frame frequency to be 240 Hz or higher.Therefore, clear pictures picked up by computer graphics or high-speedshutter video cameras can also be displayed without deterioration of thepicture quality.

In clear pictures picked up by computer graphics or high-speed shuttervideo cameras, the contours of the objects are often clear. That is, inan image pick-up method using a usual camera, the object often moveswhile the shutter of the camera is open, so that the contours of theobject in one frame picture often blur. Therefore, even if aninterpolated picture is produced by this system, effects are oftendifficult to appear.

Therefore, the spatial frequencies of one frame picture are obtained bythe Fourier transformation. When many high spatial frequencies areincluded, the refresh rate of the output frame picture is set to behigh, and when high spatial frequencies are hardly included, the refreshrate of the output frame picture is set to be low.

Since the picture jumping phenomenon does not only depend on the movingspeed of the object, but it also depend on the spatial frequency, asystem for producing an interpolated picture is preferably used whenmany high spatial frequencies are included, and a system for producing ablack raster picture is preferably used when high spatial frequenciesare hardly included.

Sixth Embodiment

Referring to FIGS. 14, 15 and 23, the sixth embodiment of an imagedisplay system according to the present invention will be describedbelow. In the image display system in the sixth embodiment, the framefrequency of the display device with a high-speed refresh rate 50 isvariable in accordance with the moving speed of a moving object, whichis included in picture information, in the image display system in thefirst or second embodiment. As described above, the moving speed of themoving object can be calculated by the processing in the motiondiscriminating part 20, e.g., by the scalar quantity of a motion vectorusing MPEG4.

For example, as shown in FIG. 23, the shape information and positioninformation of an object are inputted to the system by the contents basecoding of MPEG4. The basis of the shape information is used for dividingthe spatial frequency by the Fourier transformation in a spatialfrequency dividing part 25 to obtain a spectrum every spatial frequencyof the object, and the position information is used for obtaining themoving distance, i.e., the moving speed, of the object by the movingobject detecting part 26. The spectrum and the moving speed are inputtedto an object motion discriminating part 27 as an object motionindicating signal. Since the object motion indicating signal has thesame function as that of the display system control signal shown in FIG.1, it is also expressed as a display system control signal in FIG. 23.

A processing method in an object motion discriminating will be describedbelow. For example, when a spectrum of 3 cpd (cycle per degree) of anobject has −20 dB or less, a system for inserting a black raster pictureis used since it is difficult to visually recognize the picture jumpingphenomenon at a moving object speed of 10 deg/s, and when the spectrumhas −20 dB or higher, a system for producing an interpolated picture isused. That is, even if the moving speed is the same, when a spectrum of3 cpd of an object has −20 dB or less, the processing method, which isused when it is determined that the display picture is a slow movingpicture, is used, and when the spectrum has −20 dB or higher, theprocessing method, which is used when it is determined that the displaypicture is a rapid moving picture, is used. For example, when the abovedescribed spectrum of 3 cpd has −10 dB or less, a system for inserting ablack raster picture is used since it is difficult to visually recognizethe picture jumping phenomenon at a moving object speed of 20 deg/s, andwhen the spectrum has −10 dB or higher, a system for producing aninterpolated picture is used. Similarly, even if the moving speed is thesame, when a spectrum of 3 cpd of an object has −10 dB or less, theprocessing method, which is used when it is determined that the displaypicture is a slow moving picture, is used, and when the spectrum has −10dB or higher, the processing method, which is used when it is determinedthat the display picture is a rapid moving picture, is used. Thediscriminating method based on numeric values can be carried out bydiscriminating the motion of the object on the basis of a discriminationthreshold of visual temporal-spatial frequency characteristics.Alternatively, the discrimination can be carried out from a plurality ofnumerical values without limiting the kind of numerical values to onekind. Thus, the system has the function of selecting the interpolatedpicture or black raster picture as the output frame picture by thespatial frequency of one frame picture, so that the calculation quantityin this system can be optimized to decrease electric power consumption.

The moving speed of the moving object can be obtained by extractingcontours, obtaining the spatial frequency of fringes formed by a contourportion during a certain period of time, and obtaining a discriminationthreshold from a visual time-spatial frequency, in place of thecalculation of the moving speed of the moving object by the scalarquantity of a motion vector using MPEG4. For example, in this system,the contours of a round moving object are extracted as shown in FIG. 14to obtain a spatial frequency which is formed by contours of 3 frames(corresponding to 50 ms at a frame frequency of 60 Hz) (see FIG. 14(b)). In the display system of a frame frequency of 60 Hz, if the movingobject moves at 20 deg/s, the spatial frequency c of fringes formed byone side contour is obtained by the following expression.c=3/(20×(3/60))=3 cpd  (1)

The spatial frequency of 3 cpd is very easy to be visually recognizedfrom visual temporal-spatial frequency characteristics, so that thepicture quality deteriorates as a picture jumping. Therefore, if therelationship between the speed of the moving object and the framefrequency is obtained so that the spatial frequency thus obtained is,e.g., 12 cpd or higher, it is divided by a straight line into a region,in which it is difficult to visually recognize the picture jumpingphenomenon, and a region in which the picture jumping phenomenon mayoccur. By using this relationship, the display picture is displayed bychanging the frame frequency in accordance with the moving objectincluded in picture information.

Since pictures displayed by television generally include many movingbodies which move at 10 deg/s, the frame frequency must be 120 Hz orhigher. Since rapidly moving screens for sports or the like include manymoving bodies which move at 20 deg/s, the frame frequency is preferably240 Hz or higher.

As described above, also in the sixth embodiment, it is possible toprevent the deterioration of the picture quality.

As described above, according to the present invention, it is possibleto prevent the deterioration of the picture quality.

According to the inventor's experiment, it was confirmed that themovement of an object was displayed at intervals when a picture wasdisplayed on a monitor capable of rewriting at a high frame frequency of480 Hz, by a system in which the picture was displayed for a period ofone frame and was not displayed for a period of seven frames. On theother hand, when pictures were displayed on all of frames, the movingobject having slight blurring was observed substantially similar to thereal world. For example, the above described situation observed at afixation point is a case where character information is fedindependently of picture information displayed on a digital televisionand where characters displayed on the background image are observed, orthe like. However, according to the present invention, thesedisadvantages can be improved.

While the present invention has been disclosed in terms of theembodiment in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

1. An image display system comprising: a display device configured to display a picture while changing the picture every frame picture; an image processing device comprising a picture signal converting part configured to convert an input picture signal, which is a picture signal for a picture to be displayed on a display device configured to display a picture while changing the picture every frame picture, and an input synchronizing signal, which is synchronized with the input picture signal, into an output picture signal, which is a picture signal for a picture suitable for the display for the display device, and an output synchronizing signal which is synchronized with the output picture signal, on the basis of picture information which indicates whether the picture to be displayed on the display device is a moving picture or a still picture; and a motion discriminating part configured to discriminate whether the picture to be displayed is a moving picture or a still picture, wherein the picture signal converting part comprises: a device discriminating part configured to discriminate whether a display device is an impulse type device or not; an input frame memory configured to record an input frame picture; an input switching part configured to transmit an input frame picture to be displayed, to the input frame memory on the basis of the input picture signal and the input synchronizing signal; a black raster picture producing part configured to produce or store a black raster picture; a picture converting part configured to produce output frame pictures from input frame pictures, which have been recorded in the input frame memory, by producing an interpolated picture or inserting a black raster picture or thinning out the frame pictures, between frame pictures corresponding to the picture information, on the basis of the picture information and the input synchronizing signal and the output synchronizing signal; an output frame memory configured to record therein the output frame pictures; and an output control switching part configured to take the output picture signal and the output synchronizing signal out of the output frame pictures, which have been recorded in the output frame memory, to transmit the signals to the display device, and wherein the motion discriminating part comprises: a switching part configured to incorporate input frame pictures to be displayed, at regular intervals on the basis of the input picture signal and input synchronizing signal; a plurality of frame memories configured to store therein the input frame pictures which have been incorporated by the switching part; means for calculating a differential signal between two input frame pictures which have been continuously incorporated; and means for discriminating whether the input frame picture to be displayed is a moving picture or a still picture on the basis of the results of the calculation, wherein when it is determined that the picture to be displayed is a moving picture, the motion discriminating part determines whether the moving picture is in a first state in which the motion of a moving object in the moving picture is rapid, or in a second state in which the moving speed of the moving object is slower than that in the first state, on the basis of the correlation, and wherein when it is discriminated that the display device is the impulse type display device, when it is discriminated that the picture to be displayed is a moving picture, and when it is determined that the moving speed of the moving object in the moving picture is in the second state, the picture converting part compares the refresh rate of the input frame pictures with the refresh rate of the output frame pictures, outputs the input frame pictures as the output frame picture, when the refresh rate of the input frame pictures is equal to the refresh rate of the output frame pictures, stop the output of signals between the input frame pictures, or inserts and outputs a black raster picture, when the refresh rate of the output frame pictures is higher than the refresh rate of the input frame pictures, and thins out the input frame pictures to produce and output the output frame pictures, when the refresh rate of the output frame pictures is lower than the refresh rate of the input frame pictures.
 2. An image display system as set forth in claim 1, wherein the picture signal converting part produces the output frame pictures from the input frame pictures on the basis of a moving or still picture indicating signal, which indicates whether the kind of a picture to be displayed on the display device is a moving picture or a still picture, and the output of the motion discriminating part. 